Known sensor devices for monitoring volatile organic compounds (“VOCs”) at low parts per million (“ppm”) and ultra low parts per billion (“ppb”) concentrations have been limited to effective use for only short durations of time as a result of certain limitations of the known devices. More specifically, the known sensors cannot accurately measure the concentration of the VOCs over time, because they malfunction within a fairly short period of time and require a recalibration to accurately measure the VOC concentration. This recalibration process is tedious and requires a considerable period of time to conduct.
Known ultraviolet (“UV”) illumination systems for sensing VOCs operate by exciting electrons in VOC molecules from a lower to a higher orbital state with UV radiation. As the electrons drop back to a lower orbital state, they release a photon. Each of the known detection systems has a photon-sensitive sensor that detects the discharged photons, thereby providing a measure of the number of VOCs in the sample. One disadvantage of these known systems is that the excited VOC molecules are “sticky.” That is, the excited molecules are prone to adherence to various surfaces. As a result of this adherence property, the excited VOC molecules, over a short period of time, begin to adhere to and eventually start to cover the surface of the UV-illumination device, thereby blocking at least some portion of the UV radiation that is necessary for the sensor to operate correctly. This ongoing and continually increasing reduction of the UV radiation generated by the device causes a continual decrease or reduction in the number of excited VOC molecules, thereby resulting in skewed VOC concentration measurements that increasingly differ from the actual VOC concentration in the sample.
This known sensor limitation has restricted the measuring of low concentrations of VOCs to short and infrequent intervals. As a result of this issue, long term monitoring of VOCs has not been possible to date.
There is a need in the art for an improved VOC monitoring system that can monitor VOCs over a longer period of time in comparison to known systems.